The goal of this project is the design, synthesis and evaluation of novel heterocyclic dications for treatment of AIDS-related opportunistic diseases. Dicationic molecules synthesized in our laboratory have shown significant activity against P.carinii, C.parvum, C.neoformans and C.albicans. The proposal is based upon data, for compounds synthesized by us, obtained by other groups in our NCDDG during the current two year funding period.We have developed aryl-furan and pyrimidine diamidines which bind to AT rich minor grooves of DNA, inhibit microbial (not mammalian) topoisomerase II and show excellent in vivo activity against P. Carinii and C. parvum. DB75 is active at the nanomolar level by iv dosage and at the micromolar level on oral dosage in the in vivo immunosupressed rat PCP model. DB75 and DB100 are orally active against C. parvum in vivo at the micromolar level. Other furan diamidines show good in vitro activity against both C. neoformans and C. albicans. Our most recent results are the most exciting ones from our two years work; mono-alkyl diamidines DB181 and DB194 are quite active and non-toxic in the PCP rat model. This result opens extensive new avenues for development of anti-OI compounds including ones with improved oral activity. Collectively, our results show that use of apparent relationships between in vivo activity DNA binding and topoisomerase II inhibition is a successful strategy for development of anti-OI agents. The design of new compounds outlined herein will be guided by the above strategy and will be based upon biophysical studies and computer modeling(Wilson), biochemical and enzymological investigations(Dykstra), and in vitro and in vivo antimicrobial results(Blagburn,Hall,Perfect). Synthetic work will focus on two areas: l) new molecules designed for greater activity and less toxicity, 2) alteration of our best diamidines(or new ones that emerge) to increase oral bioavailability(prodrugs and other strategies). Fundamental elements included in new molecules are: i) radius of curvature ii) dication location and iii) inner face hydrogen bond donors, acceptors. Molecules with bulky groups on the outer face(placed to avoid adverse interactions) will be made to enhance inhibition of DNA directed enzymes. Elongated dicationic molecules will be made which cover 6-8 base pairs(current ones cover 3-4 base pairs) and will give greater binding affinity and selectivity. Two different approaches to improve oral bioavailability are proposed: a) prodrugs, b) zwitterions. The former approach will modify the amidine unit so that it is uncharged when it reaches the stomach and after passage to the blond stream esterases or other enzymes will liberate the cation. The latter strategy will use formally neutral zwitterion molecules,which show improved passage through the gut relative to cations. The majority of the morbidity and mortality in AIDS patients is attributed to the opportunistic diseases addressed by this NCDDG. The development of a single drug for treatment of more than one opportunistic infection from the diamidine class of compounds now seems a realistic possibility based upon the first two years work of this NCDDG and would be an important contribution to the therapy of AIDS patients.